This paper studies the effects of spatially uncertain material properties of composite helicopter rotors on vibratory hub load predictions. The flap, lag and torsional stiffnesses of the rotor blades are considered to vary spatially along the axis of the rotor blades. The spatial uncertainty analysis is performed with rotors modeled as both isotropic rotors and dissimilar rotor systems. In isotropic rotor systems, the uncertainty is considered to be similar for all of the four blades and the uncertainty effects on the 4/rev vibratory hub loads are studied. To reduce the computational expense of uncertainty analysis, a high dimensional model representation (HDMR) method is developed to approximate the vibratory loads as functions of blade stiffness properties modeled as random fields.